Not applicable.
The present invention relates to filters for use in removing solids from a solid/liquid mixture or metal working fluids and more specifically relates to a highly efficient filter assembly for use in swarf removal systems that can operate in large or small areas.
Many industries employ machining and grinding devices such as drills, mills, cutting devices, grinding wheels, etc., to remove metal pieces, chips, xe2x80x9cstringsxe2x80x9d and other fines from work items thereby forming the work items into final products. Hereinafter removed metal material will be referred to as swarf. To remove swarf often a liquid stream is employed that is directed at the machining point and that xe2x80x9cwashesxe2x80x9d the swarf from the machining area.
To collect the liquid for reuse a tank and conveyor are provided below the machining point. Swarf is washed into the tank and settles to the conveyor that is arranged near the bottom of the tank. Relatively heavy swarf settles quickly to the conveyor is transferred to a swarf collection bin. Smaller fines stay in suspension and eventually form a liquid/swarf mixture that is extremely xe2x80x9cdirtyxe2x80x9d. Dirty liquid cannot be used for machining or grinding purposes primarily because such liquid can clog spraying hardware, load wheels, scratch parts and cause metal working fluid degradation.
To render dirty liquid reusable most swarf handling systems include some type of filter to separate swarf from the liquid. Filtering effectiveness is extremely important as clean liquid reduces maintenance downtime, extends coolant life, improves machining precision and often extends tool life.
Many different filter configurations have been implemented. One filter configuration includes a metallic drum having small holes in the drum side wall. The drum is disposed on its side and the underside of the drum is disposed below a liquid-solid mixture level so that there is a pressure differential between the inside and outside of the drum. Liquid pours through the drum holes into the drum interior while swarf fines are stopped by the drum wall. Eventually accumulated fines form a swarf cake on the undersurface of the drum (i.e., on the submersed wall section). Liquid inside the drum is removed to maintain the differential pressure within the drum. When the holes in the underside of the drum become clogged, the drum is rotated such that an adjacent drum side faces downward and filtering continues. Pressure sensors for determining when to rotate a drum filter due to clogging are known in the art. One configuration of the above described type is described in U.S. Pat. No. 3,000,507 (xe2x80x9cthe ""507 patent) entitled xe2x80x9cRotary Filterxe2x80x9d that issued on Sep. 19, 1961.
Drum filters of the above described type have several shortcomings. First, after clogging, the holes must be cleared prior to reuse. Second, often the drum holes cannot be made small enough to remove very small fines. Third, such filters often require extended periods to filter the amount of liquid required. Fourth, such filters often must be substantially submersed (see the ""507 patent) in order to cause a required pressure differential between the inside and outside of the drum. In addition to increasing the differential pressure, many drum filter references teach that a large portion of the drum should be submersed to increase filtering area.
The industry has developed several systems for unclogging holes or removing accumulated solids from drum filters. The ""507 patent teaches a blower that blows air through drum holes from the inside of the drum thereby dislodging accumulated cake chunks and clearing the holes. A discharge chute is positioned under the discharge area so that dislodged chunks do not fall back into the tank. Unfortunately air blowers work best where drum holes are relatively large and therefore systems of this type often produce liquid that remains relatively dirty after filtering.
Another filter cleaning solution has been to provide a mechanical xe2x80x9ccake knifexe2x80x9d along a filter path and adjacent a filter surface that effectively scrapes cake chunks from the surface of the filter. While removing accumulated cakes from the surface of a filter drum, unfortunately this solution does little to clear swarf from filter holes or apertures.
One other filter cleaning or clearing solution that has been adopted by many in the industry is to provide a liquid sprayer that sprays the back surface of a filter with a clean liquid to knock accumulated cake chunks off the filter. Where liquid clearance systems are used, the tank typically is extended under the clearance area so that clearance liquid and cake chunks are redeposited in the tank after a clearing process. The cake chunks, being relatively heavy, settle to the bottom of the liquid tank. To remove the cake chunks from the tank, a conveyor or drag chain is placed along the bottom of the tank that drags the chunks therefrom to a point above a swarf bin where the chunks are deposited.
One other technique for loosening accumulated swarf cakes is to cause distortions in the shape of the filter media. To this end, after a cake has been formed, the cake naturally tends to maintain its compacted shape, even when the underlying filter shape is altered. Thus, when filter shape is altered, the cake often breaks into chunks and the chunks fall from the filter. U.S. Pat. No. 3,667,614 titled xe2x80x9cFiltering Apparatusxe2x80x9d which issued Jun. 6, 1972, teaches one configuration that relies in part on filter deformation for cake removal.
To increase filter effectiveness some configurations provide a mesh or material filter media around the drum wherein the media includes much smaller holes and tortuous paths therethrough so that even extremely small swarf bits are removed from the liquid during filtering. In these cases the filter media is typically sealed to the drum via bands adjacent the top and bottom drum ends so that swarf cannot pass into the drum without passing through the filter media. Such sealing is extremely important to ensure that only clean liquid passes through the filter.
To increase filtering speed some drum type filters increase the pressure differential between the inside and outside of the drum by removing air from within the drum to provide a vacuum therein. One patent that describes a system of this type is U.S. Pat. No. 5,954,960 (xe2x80x9cthe ""960 patentxe2x80x9d) titled xe2x80x9cRotary Drum Type Dehydratorxe2x80x9d which issued Sep. 21, 1999. While creation of a vacuum speeds up the filtering process, often, because air is pulled through the drum wall section that is not submersed while liquid passes through the submersed wall section, the vacuum is relatively ineffective unless a massive and, in some cases, prohibitively expensive pump is employed. The ""960 patent relies in part on the presence of a built up cake on the un-submersed section of the drum to increase the vacuum effect. Nevertheless, in order to facilitate efficient filtering typically the filter media should be rotated prior to complete clogging of the media (i.e., filtering efficiency is substantially reduced prior to complete clogging). Thus, the cake that accumulates prior to drum rotation typically is insufficient to block air from entering the inside of the drum.
In addition to drum type filters other filter configurations have been developed that use a vacuum inside a filter chamber to increase filtering speed. U.S. Pat. No. 4,242,205 (xe2x80x9cthe ""205 patentxe2x80x9d) teaches a filter box submersed inside a liquid-solid mixture tank wherein an upper wall of the box forms an opening and a flexible filter belt is arranged so that a portion of the belt covers the opening. The belt is periodically slid across the opening so that different filter sections cover the opening at different times and a liquid sprayer is used to clean the soiled filter sections. A vacuum is formed inside the box. In this case, because the filter box has only a single open wall a relatively small pump can be used to generate a vacuum in the box thereby increasing filtering speed.
Unfortunately, the ""205 patent configuration also has several shortcomings. First, the ""205 patent configuration requires a complex sealing configuration to seal the filter belt to the edges of the box about the opening. To this end the ""205 patent configuration requires, among other things, two hold down chains linked to drive belt chains.
Second, the ""205 patent configuration teaches a relatively complex belt path that increases hardware requirements and the space required to accommodate the configuration. Additional hardware for sealing and path configuration increase system costs appreciably.
Third, while the ""205 patent configuration seal may operate properly while a vacuum is formed in the filter box, the ""205 patent configuration requires that the vacuum be broken prior to movement of the filter belt. After breaking the vacuum the filter belt is slid across the filter box edges which means that the sealing pressure holding the belt to the box has to be extremely small. If the sealing pressure were large the belt would likely wear and eventually tear as the belt is slid across the box opening. However, it is believed a smaller sealing pressure that would allow the ""205 patent configuration belt to slide against the opening would be insufficient to block xe2x80x9cdirtyxe2x80x9d liquid from entering the filter box during belt movement.
Fourth, as indicated above, the ""205 patent configuration also requires that at least one opening face upward. For this reason the ""205 patent configuration requires that the filter be completely submersed. This limitation requires that the liquid level in the tank be at least as high as the filter box depth and some clearance thereunder for a drag chain to drag cake chunks out of the box.
Thus, there is a need for a swarf filtering configuration that removes extremely small swarf fines from liquid-solid mixtures relatively quickly, automatically replaces clogged filter media with clean media, automatically cleans clogged media and achieves all of the above goals relatively inexpensively and using hardware that is relatively small and that enables operation with a low tank liquid level.
It has been recognized that many of the disadvantages associated with the prior art can be overcome by providing a filter loop that is sealed at opposite ends to first and second housing walls wherein the loop is oversized so that the loop is loose or slack between the walls and about a girth around a central portion of the loop and providing a suction assembly including a header within the loop wherein the suction header defines both a reduced size suction chamber and an opening that opens into the chamber where a section of the loop covers the opening and the opening is positioned within a mixture tank below the mixture level.
With a system as described above, the suction assembly increases the speed with which liquid can be filtered through the loop section adjacent the opening. It has been found that such a system can increase the liquid filtering rate to rates much higher than the rates achievable where much greater sections of a filter drum are submersed.
In addition, with the system above, where the opening faces downward, the mixture level in the tank can be relatively low and still accommodate the filter configuration. A low mixture level means the tank size can be reduced in certain applications and that less liquid is required to facilitate the machine process.
Moreover, the excess pressure caused by the reduced size suction chamber causes accumulation of tightly packed solid cakes on the filter loop that are heavier than cakes formed via other filter systems. When forced off the loop, the heavier cakes sink more readily within the tank liquid and do not disintegrate as readily in the tank prior to removal via a drag chain or conveyor.
Furthermore, by providing sealing the loop to the housing edges essentially no unfiltered liquid can enter into the filter chamber.
With the present invention the loop is sealed to housing wall edges during both filtering periods and loop movement periods to ensure that no dirty liquid passes into the suction chamber (or filtering chamber for that matter).
Moreover, by providing an oversized filter loop, when the vacuum is turned off so that the suction stops, the loop becomes slack adjacent the header and the filter loop can be moved with respect to the header without damaging the filter loop. Then, when the suction is again caused, the filter section adjacent the opening is sucked against the header for support. One embodiment of the header includes a support screen across the opening to support the filter loop.
The invention also includes a method wherein, with the configuration described above, with the opening below the mixture level suction is caused at the opening to begin the filtering process and after a condition related to filtering efficiency is sensed, the support housing and sealed filter are rotated until another filter loop section is adjacent the opening. Here the suction header remains stationary while the housing and loop are rotated.
With the present filter assembly filtering speed can be increased in two different ways. First vacuum suction can be increased. Second, support housing and sealed loop rotation frequency can be increased. By combining both suction and rotation frequency increases overall filtering speed is increased appreciably.
In one embodiment the invention includes a filter apparatus for separating liquid from solids in a tank, a liquid/solid mixture disposed in the tank in an amount such that the mixture rises to a mixture level within the tank and the apparatus comprises a housing formed about a chamber including first and second oppositely facing walls characterized by first and second wall edges the walls separated by at least one cross-member. The distance between the first and second walls defines a first dimension. A suction assembly includes a header forming an opening having an opening width and an opening length, the assembly supported in the chamber and juxtaposed with the tank such that the opening is below the mixture level. A filter loop has oppositely facing loop edges, the loop having first and second peripheral portions adjacent the loop edges and having a loop width between the first and second peripheral portions that is greater than the first dimension. The first and second peripheral portions are sealed against the first and second wall edges, respectively, such that the filter surrounds the chamber, a filter section is adjacent the opening, the filter width is between the walls and the filter is slack along the width dimension. A vacuum is linked to the assembly for causing suction at the opening. A motivator is provided for moving the loop with respect to the opening. A controller controls the vacuum and the motivator to periodically reduce suction at the opening and to move the loop adjacent the opening so that different loop sections cover the opening at different times.
In one aspect a belt girth length around the central portion is greater than the loop edge length. The walls may be essentially circular and the at least one cross-member includes at least first, second and third crossbars that traverse the distance between the first and second walls and may be linked to the walls adjacent the wall edges and such that the cross-members are essentially equispaced about the periphery of each of the walls.
In one embodiment the apparatus further includes first and second bands that seal the peripheral portions to the wall edges.
The header may be characterized by a semi-cylindrical shape having a radius of curvature essentially equal to the radius of curvature of each of the walls and having a length essentially equal to the distance along a wall edge between adjacent crossmembers. The controller may control the position of the housing such that adjacent crossbars are on opposite sides of the opening whenever the suction level is increased to the second suction level.
In one embodiment the combined distances between the first and second crossmembers, the second and third crossmembers and the third and first crossmembers comprise a support dimension and the support dimension is less than the wall edge length.
In another embodiment the suction assembly includes first and second facing end plates and a media support screen that traverses the distance between the end plates, the support screen covering the opening. The suction assembly may further include guide bearings adjacent the support screen for guiding the loop therealong during movement.
In another aspect the assembly may further include a clearing assembly for removing solids deposited on the loop, the clearing assembly linked to the processor and disposed adjacent the loop along the path of loop movement from the suction assembly, the controller controlling the clearing assembly to periodically disturb the solids deposited on a loop section adjacent the clearing assembly. One advantageous clearing assembly is a spray assembly comprising a liquid source linked to a spray nozzle, the nozzle disposed adjacent the loop and inside the chamber, the controller controlling the spray assembly to periodically spray liquid toward an adjacent loop section to disturb solids deposited thereon.
In another embodiment a sensor is linked to the processor for determining and indicating when at least one condition related to filtering efficiency has occurred, and when the at least one condition has occurred, the processor causes the motivator to move the loop with respect to the opening. The sensor may sense vacuum pressure.
In yet one more embodiment the configuration includes a disposable filter assembly including a support assembly, a filter ribbon, and a second motivator, the support assembly supporting a ribbon section adjacent the header on a side of the loop section adjacent the header opposite the header, the second motivator linked to the ribbon for moving the ribbon with respect to the header so that different ribbon sections are adjacent the header at different times, the controller linked to the second motivator for periodically moving the ribbon, a used end of the ribbon fed into a disposal bin.
In addition to a complete filtering system the invention also includes a filter apparatus for use with a filter assembly, the assembly including a filter housing having first and second oppositely facing walls and at least one crossbar therebetween, the first and second walls having first and second edges, each edge characterized by a peripheral housing length, the distance between the housing edges defining a housing width, the filter apparatus comprising a flexible filter loop characterized by a loop width between oppositely facing first and second loop edges, each of the first and second loop edges characterized by a peripheral loop length, the peripheral loop lengths each essentially the same length as the peripheral housing lengths, the belt having a girth length about a central portion of the belt between the first and second loop edges that is greater than the peripheral loop length and having a width between the first and second loop edges that is greater than the housing width such that when the first and second loop edges are sealed to the first and second housing member edges the loop is slack between the first and second housing member edges and around the central belt portion.
The filter apparatus is also for use with a suction assembly and a vacuum, the suction assembly disposed inside the filter housing, the suction assembly including a header that defines a suction opening, the vacuum linked to the header for creating suction at the opening, the loop length and width such that a loop section adjacent the opening is slack when the vacuum is off and is sucked up against the header when the vacuum is on.
The invention further includes an apparatus for supporting a flexible filter belt loop, the loop characterized by a loop width between oppositely facing first and second loop edges. In this regard the support apparatus includes first and second oppositely facing housing walls characterized by first and second peripheral edges, respectively, each edge characterized by a peripheral housing length and formed so that one of the loop edges is sealable thereto and at least one crossmember linked to and between the first and second walls such that the distance between the housing edges defines a housing width, the crossmember having a cross sectional area substantially less than the surface area of each of the first and second walls. In one such embodiment each of the walls is essentially circular and the at least one crossmember includes first, second and third crossmembers that traverse the distance between the walls, the crossmembers linked to the walls adjacent the wall edges and equispaced about the edge peripheries.
The invention further includes a filter apparatus for separating liquid from solids in a tank, a liquid/solid mixture disposed in the tank in an amount such that the mixture rises to a mixture level within the tank, the apparatus comprising: a housing formed about a filter chamber including first and second oppositely facing walls having by first and second wall edges, respectively, the walls separated by at least one crossmember, the filter chamber having a first volume; a suction assembly including a header forming a suction chamber having a second volume that is substantially less than the first volume, the header forming an opening that opens into the suction chamber, the assembly supported in the chamber and juxtaposed with the tank such that the opening is below the mixture level; a filter loop having oppositely facing loop edges, the loop having first and second peripheral portions adjacent the loop edges, the first and second peripheral portions sealed against the first and second wall edges, respectively; a vacuum linked to the assembly for causing suction at the opening; a motivator for moving the loop with respect to the opening and a controller for controlling the vacuum and the motivator to periodically reduce the suction at the opening from the second to the first suction level and move the loop adjacent the opening so that different loop sections cover the opening at different times.
Thus, it has also been recognized that while a small suction chamber limits the amount of filter loop used at any given time for filtering purposes, a small suction chamber results in greater suction through the used filter section such that the overall amount of liquid filtered in a given period can be increased appreciably. Because filtering speed is increased the amount of cooling liquid required, reduces tank size, can in fact increase filtering speed, etc.
These and other objects, advantages and aspects of the invention will become apparent from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention and reference is made therefore, to the claims herein for interpreting the scope of the invention.